INSIDIOUS Synonyms: 100 Similar and Opposite Words

insidious

adjective

Definition of insidious

as in treacherous

formal causing harm in a way that is gradual or not easily noticed Most people with this insidious disease have no idea that they are infected. an insidious enemy

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Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of insidious Duckworth also faced backlash from critics who argued that her message was, at best, a series of hollow exhortations to simply try harder and, at worst, an insidious form of victim-blaming that ignored structural inequality. — Meghan O’Gieblyn, New Yorker, 14 Sep. 2026 If anything, this makes those insidious Fridays insignificantly safer than the state average for the period. — Mike McRae 08, New Atlas, 8 Sep. 2026 Growing up in Beverly, Frates – the warrior against ALS who succumbed to the insidious disease in 2019 – was a huge fan of the Bruins’ star and had a poster of the defenseman in his room. — Steve Conroy, Boston Herald, 6 Sep. 2026 But the insidious harm that moves in the other direction — from illness, through a patient, into the person treating her — has no forum at all. — Jennifer Adaeze Okwerekwu, STAT, 1 Sep. 2026 See All Example Sentences for insidious

Recent Examples of Synonyms for insidious

Adjective

Time is running out for a Republican Party led astray by a president whose treacherous behavior mimics those assigned to the lowest level of Dante’s hell.

— Bob Kustra, Chicago Tribune, 22 Oct. 2026
Russell doesn’t traffick in any of that, and screenwriter Christopher Logue refuses to pathologize the two, focusing instead on the untamed beauty of their relationship, which was romantic, familiar, treacherous, and pure.

— Juan A. Ramírez, Vulture, 20 Oct. 2026

Definition of treacherous

Adjective

The rash can be more subtle on darker skin tones, but a bumpy or textured feel is often present.

— Sara Tenenbaum, CBS News, 21 Oct. 2026
The last major change was the iPhone X, which dropped the home button almost a decade ago, and even that was a fairly subtle improvement.

— Nilay Patel, The Verge, 21 Oct. 2026

Definition of subtle

Adjective

But several Theranos staffers and journalists say Holmes was frequently deceptive and would lie repeatedly, especially when confronted with facts.

— Los Angeles Times, Los Angeles Times, 21 Oct. 2026
California and Hawaii, for example, are two states that have banned sharing deceptive AI content about candidates in the months around an election.

— Jordi Calvet-Bademunt, The Conversation, 20 Oct. 2026

Definition of deceptive

Adjective

Experts worry federal law enforcement could potentially use those false claims — or others generated this year — as pretext to try to seize ballots during the counting period, or interfere in the process in some other way.

— Miles Parks, NPR, 22 Oct. 2026
The false polling data from Wedgewood Polls consistently favored Democrats, particularly progressive candidates.

— Hailey Bullis, The Washington Examiner, 22 Oct. 2026

Definition of false

Adjective

Meta argued the state failed to prove misleading statements about privacy and that content moderation actually harmed New Mexicans.

— ABC News, ABC News, 21 Oct. 2026
Meta argued that New Mexico failed to prove that the tech giant's executives made misleading statements about privacy and that its content moderation practices harmed state residents.

— Aimee Picchi, CBS News, 21 Oct. 2026

Definition of misleading

Adjective

Hanuman inspires him to avenge the rape of his mother by a corrupt policeman working for a deceitful Hindu nationalist spiritual leader.

— Sohini Sarah Pillai, The Conversation, 14 Oct. 2026
Magpies are opportunistic scavengers, incredibly cunning and deceitful and capable of calculated deception.

— Voice of the People, New York Daily News, 28 Sep. 2026

Definition of deceitful

Adjective

The reality, of course, is that the Southern accent is not some incorrect version of a national standard but instead a historically separate and unique dialect – or, more accurately, set of dialects.

— Valerie M. Fridland, The Conversation, 20 Oct. 2026
And Ballmer and the Clippers remain adamant the penalties—and the allegations of misconduct—are incorrect.

— Joshua Hong, Fortune, 20 Oct. 2026

Definition of incorrect

Browse Nearby Words

inside tracks

insidious

insidiously

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Style

“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 25 Oct. 2026.

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Synonyms of insidious

adjective

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